A Los Angeles District Attorney (Gene Hackman) is attempting to take an unwilling murder witness (Anne Archer) back to the United States from Canada to testify against a top-level mob boss. Frantically attempting to escape two deadly hit men sent to silence her, they board a Vancouver-bound train only to find the killers are on board with them. For the next 20 hours, as the train hurls through the beautiful but isolated Canadian wilderness, a deadly game of cat and mouse ensues in which their ability to tell friend from foe is a matter of life and death.

Martin Brundle, born of the human/fly, is adopted by his father’s place of employment (Bartok Inc.) while the employees simply wait for his mutant chromosomes to come out of their dormant state.